So I noticed that all of the sounds are in English.
Are there some GPL sounds in Russian and German that could replace those? Or is there a native speaker of those languages willing to record some replacement sounds?

No not really. I'm not even sure I would use the stuff once I had it. There's something odd about playing a game from the perspective of Stalin or Hitler; I think I'd be more comfortable playing as orcs or undead or something. I just figured the game could be improved if someone tackled the sounds, and it seems like it wouldn't be hard to implement once the sounds were made. I guess a translation of the mission briefings and the creation of campaigns would be more important if someone were to update the game.